This invention relates generally to apparatus for the measurement of optical energy and more particularly to a means for determining the Stokes parameters of extremely short optical pulses in the nanosecond (1.times.10.sup.-9 seconds) of a laser beam.
Previous methods for the determination of polarization of an optical beam assume continuous (CW) operation. Apparatus known as rotating ellipsometers is adapted to determine the polarization; however, it is relatively slow. Current applications of laser beams, however, require a very short "look" time and thus prior art apparatus is not readily adapted to characterize completely the polarization state of laser pulses of ultra short duration time.
As noted above, the polarization state of an optical beam can be determined by traditional ellipso-metric techniques. The inventor is aware of these publications describing such techniques. The first is an article entitled "AIDER: Angle-Of-Incidence Derivative Ellipsometry and Reflectometry" by R. Azzam, which appeared in Optics Communications, January, 1976, at page 153. The second comprises the proceedings of the Symposium On Recent Developments In Ellipsometry, (N. Holland, 1968) by N. Bashara, et al. and the third is an article entitled "Photometric Ellipsometer for Measuring Partially Polarized Light" by D. E. Aspnes which appeared in the Journal of the Optical Society of America, Vol. 65, Nov. 1975 at pp. 1274-1278.
The techniques disclosed in the prior art have basically evolved for DC and CW optical sources. With the introduction of laser sources, however, pulse widths of the order of nanoseconds (10.sup.-9 secs.) can be generated. Because of these extremely short pulse widths it becomes impossible to analyze the optical field to determine its polarization state using ordinary methods of measurement. Basically the problem is the same, however, which is to determine the polarization state as represented by the Stokes parameters of the generated pulse.